1. Field of the Invention
The present invention relates generally to nitride-based semiconductor light-emitting devices and particularly to those formed on a Si substrate.
1. Description of the Background Art
Conventionally, quarternary AlGaInN compounds are used to fabricate on a sapphire substrate, a GaN substrate or a SiC substrate a light-emitting device using InxGa1xe2x88x92N epitaxial films as a light emitting layer.
A Si substrate is inexpensive, has high quality and also can provide a substrate of a large area and using the Si substrate allows the semiconductor light-emitting device to be fabricated at a cost lower than when a conventional substrate is used.
As a technique used to fabricate a nitride on a Si substrate, Japanese Patent Laying-Open No. 5-343741 discloses that AlN is used as an intermediate layer and thereon the nitride-based semiconductor is grown.
However, the intermediate layer of AlN has high resistance, and inspite that the conductive substrate of Si is used, electric current cannot be introduced from under the substrate through the intermediate layer into the nitiride-based semiconductor.
Accordingly the present inventors tried to use an intermediate layer of AlGaN to provide a level of resistance lower than AlN. Doping an AlGaN layer with Si and growing the same at a high temperature of no less than 1000xc2x0 C. allowed the grown intermediate layer to have a low resistance. Growing the layer at the high temperature of no less than 1000xc2x0 C., however, results in the Si substrate having a surface with nitride film formed thereon.
This nitride film has high resistance and it is thus still difficult to introduce electric current from under the Si substrate into the nitride-based semiconductor.
Furthermore, to further reduce the AlGaN layer in resistance the layer needs to have a higher Ga content, although if AlGaN with a large Ga content is provided directly on a Si substrate, at a high temperature Si and Ga react with each other and the Si substrate would have an interface etched, and flat and satisfactory film for semiconductor light-emitting devices can hardly be obtained.
Accordingly the present inventors tried to grow an intermediate layer of AlGaN at low temperature to prevent nitrification of the interface. For an intermediate layer of AlGaN formed at a low temperature of no more than 950xc2x0 C., semiconductor film formed thereon was hardly flat.
Thus, if an AlGaN layer is used as an intermediate layer, for high-temperature growth the Si substrate would have a nitrided interface and for low-temperature growth the issue of planarity is concerned.
The present invention has been made to overcome the disadvantages described above. More specifically the present invention contemplates a nitride-based semiconductor device. of high quality fabricated on a Si substrate and capable of electrical conduction from the Si substrate.
The present invention provides a semiconductor light-emitting device including: a Si substrate, a nitride-based semiconductor of a first conductivity type formed successively on the Si substrate, a light emitting layer formed successively on the nitride-based semiconductor of the first conductivity type, and a nitride-based semiconductor of a second conductivity type formed successively on the light emitting layer, wherein between the Si substrate and the nitride semiconductor of the first conductivity type there exists an intermediate layer formed of AlxGayInzN, wherein x+y+z=1, 0xe2x89xa6yxe2x89xa60.5, and 5/95xe2x89xa6z/xxe2x89xa640/60.
In the present device the intermediate layer is of N-type conductivity.
In the present device the intermediate layer is doped with Si.
In the present device the intermediate layer has an Al content x increased toward the Si substrate.
In the present device the Si substrate has a first electrode receiving electric current in turn passed through the intermediate layer and thus introduced into the light emitting layer to provide light emission.
In the present device the intermediate layer has a thickness in a range of 5 nm to 26 nm.
The present invention provides a method of manufacturing a semiconductor light-emitting device, including the steps of: growing an intermediate layer formed of AlxGayInzN on a Si substrate, wherein x+y+z=1, 0xe2x89xa6yxe2x89xa60.5, and 5/95xe2x89xa6z/xxe2x89xa640/60; and growing a nitride-based semiconductor on the intermediate layer.
In the present method the intermediate layer is formed at a temperature of 400xc2x0 C. to 950xc2x0 C. it, In the present method the intermediate layer is doped with Si when the intermediate layer is being grown.
In the present method the intermediate layer is grown at a rate in a range of 10 nm/hour to 1000 nm/hour.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.